Factors Affecting Longevity

Natural processes of wear in a thatched roof

Straw and or water reed are biological materials, which under any conditions will gradually wear through the actions of weathering and the processes natural, gradual decay, and from time to time it will require maintenance or to be replaced. Many roofs are re-thatched while they still have a useful life remaining; the tendency is to apply a spar coat when the roof starts to look “untidy”, the reality is that a scruffy roof that is keeping the property warm and dry is fulfilling its intended function of keeping water out.

THATCH LIFE EXPECTANCY

Many factors contribute to the life expectancy and durability of individual thatched roofs and it is the maintenance history of each property that should be considered in predicting life expectancy for its thatch. The charm of owning a thatched property is that each one is unique and will be subject to its own set of conditions which influences the life expectancy of the roof.

Local conditions

Geographical location will influence the life of a roof; thatch tends to have a shorter life expectancy in the wetter Southwest of the UK than in East Anglia. Wooded areas, overhanging trees valley bottoms, embankments and proximity of a river or ponds will also adversely affect the life of a thatched roof.

Aspect

The north side of a thatched roof will outlast a south or west facing aspect. In seasons of normal rainfall and prevailing weather patterns the north side is not subjected to such environmental extremes, but because sunlight is often restricted the north side may support the growth of algae and moss. It is the effects of frost and moisture movement, triggered by early morning sunshine that reduces the life of a south facing roof

Climate

It can be expected that a thatch wearing normally will be wet after rain at the surface and to a depth of 2cm, but even after continuous heavy rain the moisture content below the surface and deeper inside the thatch will be less than17%, the moisture content below witch the growth of micro-organisms is slowed down.

Thatching techniques

The minimum pitch for a thatched roof is 45o, old properties with multi layers of thatch can lose pitch over time as more layers are added; with the consequence that water is not easily shed and the roof remains wet and may deteriorate more rapidly.

Birds and vermin

Many thatched roofs are protected with netting to restrict access to birds, squirrels, or rats. Wire netting is a relatively modern invention; although it is a form of protection unavailable to our ancestors, under conservation terms, it is an acceptable addition to a modern thatched roof.